Liquid crystal display device and manufacturing method therefor

ABSTRACT

A liquid crystal display device includes a first substrate and a second substrate which sandwiches a liquid crystal between itself and the first substrate, wherein 
     the first substrate has thin film transistors and a wiring connection portion in which are formed terminals connected to the thin film transistors, 
     a wiring substrate connected to the terminals is disposed in the wiring connection portion, 
     the second substrate is a plastic substrate, and has an adhesive layer and an inorganic insulating layer formed on top of the adhesive layer, and 
     the adhesive layer covers the wiring connection portion and one portion of the wiring substrate.

The present application claims priority from Japanese applicationsJP2008-043293 filed on Feb. 25, 2008, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a display device, and particularly, toan ultrathin, lightweight and flexible liquid crystal display device anda manufacturing method thereof.

2. Related Art

A so-called flat panel type display device, such as a liquid crystaldisplay device or an organic EL display device, is configured of onesubstrate (an active matrix substrate or a TFT substrate), on which isformed a thin film transistor (TFT) circuit, and an opposite substrateor a sealing substrate, which holds a liquid crystal layer or anemitting layer between itself and the TFT layer. It is common that aglass material is used for these substrates. In particular, the TFTsubstrate requires a high temperature process in a TFT formation.Consequently, a glass substrate is used which is of an inexpensivematerial having a heat resistance and a low heat expansion coefficient.However, glass being fragile, there is a limitation in reducing athickness of the substrate, posing an impediment to promoting areduction in thickness and weight, and an increase in flexibility, ofthe display device.

FIG. 6 is a plan view of a heretofore known liquid crystal displaydevice. Also, FIG. 7 is a sectional view taken along line X-X′ of FIG.6. The liquid crystal display device shown in FIG. 6 is configured bysealing a liquid crystal LC between a principal surface of a thin filmtransistor substrate (a TFT substrate) SUB1, which is a first glasssubstrate, and a principal surface of an opposite substrate (a colorfilter substrate or a CF substrate) SUB2, which is a second glasssubstrate, and bonding the thin film transistor substrate SUB1 and theopposite substrate SUB2 together with a seal agent SL. Thin filmtransistors TFT, unshown pixel electrodes, and an unshown wiring systemare formed on the principal surface of the thin transistor substrateSUB1. A color filter CF divided into segments by an unshown black matrixor, in a case of a TN type liquid crystal display device, oppositeelectrodes (not shown) are formed on the principal surface of theopposite substrate SUB2.

One edge of the opposite substrate SUB2 is slightly retracted from acorresponding edge of the thin film transistor substrate SUB1, exposingone portion of the principal surface of the thin film transistorsubstrate SUB1. A wiring connection portion TMA is formed in the exposedportion. A wiring substrate FPC is connected to the wiring connectionportion TMA. The wiring substrate FPC is a so-called flexible printedsubstrate, and one extremity thereof is connected to the wiringconnection portion TMA of the thin film transistor substrate SUB1, whilethe other extremity is connected to an external circuit.

As heretofore described, a semiconductor thin film for a thin filmtransistor circuit is formed on the thin film transistor substrate SUB1,but as a high temperature process is required in this formation step, aglass substrate is used as the substrate. For this reason, in order tobend the display device, it is necessary to make the glass substratethin. However, as shown in JP-A-2005-115087, as there is a limitation inreducing a thickness of the glass substrate, there is also a limitationon a bending degree of the display device.

A flexible display device which can be freely bent cannot be made usingthe glass substrate. For this reason, as shown in JP-A-7-140451, thedisplay device can be freely transformed by using a plastic substrate.

However, the plastic material having no heat resistance, it is hard toform a high performance semiconductor thin film, and it is difficult touse the plastic substrate as a TFT substrate to which is applied thehigh temperature process which forms the semiconductor film for the thinfilm transistor circuit.

SUMMARY OF THE INVENTION

An object of the invention is to provide a liquid crystal display devicewhich makes a plastic substrate a component member with no relationshipto a high temperature process which forms a semiconductor film.

The liquid crystal display device of the invention includes aninsulating substrate on which are formed pixels having thin filmtransistors, wherein the insulating substrate has a first substrate, onwhich is provided a thin film transistor circuit including a pixelcircuit, and a second substrate which sandwiches and seals a liquidcrystal layer between itself and the first substrate.

Then, it has a feature such that, the second substrate, or both thefirst substrate and the second substrate are formed of plasticsubstrates, a principal surface of the first substrate has a siliconlayer attached thereto with a first adhesive, and the thin filmtransistor circuit and a wiring connection portion, to which isconnected a wiring substrate which, being led outside a display areafrom the thin film transistor circuit across a seal agent, inputssignals and voltages for a display from an external circuit, areprovided on the silicon layer, while a principal surface of the secondsubstrate has a silicon layer attached thereto with a second adhesive, acolor filter layer is provided on the silicon layer, and the secondadhesive fills a space outside the seal agent between the firstsubstrate and the second substrate, covering the wiring connectionportion and the wiring substrate connected to the wiring connectionportion.

In a manufacturing of the liquid crystal display device, one or both ofthe first substrate and the second substrate are formed of glasssubstrates. In this condition, of the first substrate and the secondsubstrate, one or both glass substrates are chemically or mechanicallyremoved, and plastic substrates or polarizing plates are affixed. Also,in the case in which one glass substrate is processed in this way, theother glass substrate is also chemically or mechanically removed, and aplastic substrate or a polarizing plate is affixed, thereby forming aliquid crystal display device in which both substrates are configured ofthe plastic substrates.

By it being possible to make the display surface of the display devicecurved, a flexibility of the display device is improved. By this means,a design selectivity of the display device is increased. Also, afunctionality, a weight saving and a miniaturization can be realized.The invention, not being limited to the liquid crystal display device,can also be similarly applied to a flat type of display device, such asan OLED (an organic EL display) or an FED (a field emission display).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a liquid crystal display device illustrating anembodiment 1 of a display device of the invention;

FIG. 2 is a sectional view taken along line X-X′ of FIG. 1;

FIGS. 3A to 3H are views illustrating a method of manufacturing theliquid crystal display device described in the embodiment 1 of theinvention;

FIG. 4 is a sectional view of a liquid crystal display deviceillustrating an embodiment 2 of the display device of the invention;

FIGS. 5A to 5E are views illustrating a method of manufacturing theliquid crystal display device described in the embodiment 2 of theinvention;

FIG. 6 is a plan view of a heretofore known liquid crystal displaydevice; and

FIG. 7 is a sectional view taken along X-X′ of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, a detailed description will be given of most preferredembodiments of the invention, referring to the drawings thereof.

Embodiment 1

FIG. 1 is a plan view of a liquid crystal display device illustrating anembodiment 1 of a display device of the invention. FIG. 2 is a sectionalview taken along line X-X′ of FIG. 1. The liquid crystal display deviceof the embodiment 1 shown in FIG. 1 is configured by sealing in a liquidcrystal LC between a principal surface of a TFT side flexible substrateF-SUB1, which is a first plastic substrate, and a principal surface of aCF side flexible substrate F-SUB2, which is a second plastic substrate,and bonding them together with a frame shaped seal agent SL encircling adisplay area.

A feature of the embodiment lies in adopting a structure in which awiring substrate FPC is sandwiched between the TFT side flexiblesubstrate F-SUB1 and the CF side flexible substrate F-SUB 2.

As shown in FIG. 2, on the principal surface of the TFT side flexiblesubstrate F-SUB1 is formed a silicon nitride layer (a second etchstopper layer HFS2 to be described hereafter) which, being a transparentinorganic insulating layer, is attached thereto with an adhesive SL-1.Also, a pixel circuit, configured of thin film transistors TFT, and awiring connection portion TMA are formed on the silicon nitride layer. Aplurality of terminals led outside the display area from the pixelcircuit, configured of the thin film transistors TFT, across the sealagent SL are formed in the wiring connection portion TMA. Furthermore, awiring substrate (a flexible printed substrate) FPC, which inputssignals and voltages from unshown external circuits (a display controlcircuit substrate and a TCON substrate), is connected to the pluralityof terminals.

Also, the principal surface of the CF side flexible substrate F-SUB2 hasa transparent silicon nitride layer (a second etch stopper layer HFS2 tobe described hereafter) attached thereto with a second adhesive SL-2,and a color filter layer CF is provided on the silicon nitride layer.The second adhesive SL-2 fills a space outside the seal agent SL betweenthe TFT side flexible substrate F-SUB1 and the CF side flexiblesubstrate F-SUB2, covering the wiring connection portion TMA and thewiring substrate (the flexible printed substrate) FPC.

The seal agent SL, and the first adhesive SL-1 and second adhesive SL-2,are made of different materials. It is desirable that the seal agent SLis made of a material which does not contaminate the liquid crystal.Then, it is desirable that the first adhesive SL-1 and the secondadhesive SL-2 are made of a transparent material having a bendableproperty. This is because the liquid crystal display of the invention issupposed to be a flexible display of which a display surface isbendable. Furthermore, it is desirable that the first adhesive SL-1 andthe second adhesive SL-2 are made of a material having a characteristicof preventing moisture from entering a liquid crystal layer.

FIGS. 3A to 3H are views illustrating a method of manufacturing theliquid crystal display device described in the embodiment 1 of theinvention. FIG. 3A, being a sectional view of a condition in which athin film transistor substrate SUB1 and an opposite substrate SUB2 arecaused to face each other, shows a condition before the liquid crystalis sealed in. The first etch stopper layer HFS1 and the second etchstopper layer HFS2 are laminated, in this order, onto a principalsurface of the thin film transistor substrate SUB1. The pixel circuitconfigured of the thin film transistors TFT is formed on the second etchstopper layer HFS2.

The first etch stopper layer HFS1 and the second etch stopper layer HFS2are also laminated, in this order, onto a principal surface of theopposite substrate SUB2. A color filter is formed on the second etchstopper layer HFS2. An illustration of a black matrix or the likeprovided on the opposite substrate SUB2 is omitted. Also, an orientedfilm is formed as a topmost layer on each substrate, but an illustrationis omitted here. The seal agent SL is formed encircling the display areaof the thin film transistor substrate SUB1. The wiring substrate FPC isattached to the wiring connection portion TMA at one edge of the thinfilm transistor substrate SUB1.

Mo—W is suitable for the first etch stopper layer HFS1, while siliconnitride is suitable for the second etch stopper layer HFS2. The firstetch stopper layer HFS1 is insoluble in an etchant for a glasssubstrate. Also, the second etch stopper layer HFS2 is insoluble in anetchant for the first etch stopper layer HFS1.

As shown in FIG. 3B, the principal surface of the opposite substrateSUB2 and the principal surface of the thin film transistor substrateSUB1 are bonded together, and the liquid crystal LC is sealed in withina bonding space. A perimeter of the space between the two substrates issealed with the seal agent SL.

In this condition, the opposite substrate SUB2 is dissolved and removed,by a full etching, with a glass dissolving etchant. At this time, anetching of the CF side second etch stopper layer HFS2 is stopped by theCF side first etch stopper layer HFS1 (FIG. 3C).

Next, the CF side first etch stopper layer HFS1 is dissolved and removedby a full etching (FIG. 3D). An etchant etching the CF side first etchstopper layer HFS1 does not etch the CF side second etch stopper layerHFS2. That is, the color filter CF is protected by the CF side secondetch stopper layer HFS2.

The CF side second adhesive SL-2 is applied covering the CF side secondetch stopper layer HFS2, the wiring connection portion TMA, and oneportion of the wiring substrate FPC. The CF side flexible substrateF-SUB2, which is the plastic substrate, is attached with the secondadhesive SL-2 (FIG. 3E).

By the second adhesive SL-2 covering a terminal portion of the wiringsubstrate FPC, a stress concentration on the terminal portion of thewiring substrate FPC is avoided.

Next, the thin film transistor substrate SUB1 is dissolved and removed,by a full etching, with a glass dissolving etchant. At this time, anetching of the TFT side second etch stopper layer HFS2 is stopped by theTFT side first etch stopper layer HFS1 (FIG. 3F).

Next, the TFT side first etch stopper layer HFS1 is dissolved andremoved by a full etching (FIG. 3G). An etchant etching the TFT sidefirst etch stopper layer HFS1 does not etch the TFT side second etchstopper layer HFS2. That is, the thin film transistors TFT are protectedby the TFT side second etch stopper layer HFS2.

The first adhesive SL-1 is applied covering the TFT side second etchstopper layer HFS2. The TFT side flexible substrate F-SUB1, which is theplastic substrate, is attached with the first adhesive SL-1 (FIG. 3H).

It is possible, through the heretofore described steps, to obtain theliquid crystal display device described in the embodiment 1 of theinvention.

Embodiment 2

Next, a description will be given of an embodiment 2 of the invention.

FIG. 4 is a sectional view of a liquid crystal display deviceillustrating the embodiment 2 of the display device of the invention.FIG. 4 corresponds to the section taken along line X-X′ of FIG. 1. Theliquid crystal display device of the embodiment 2 shown in FIG. 4 isconfigured by sealing in a liquid crystal LC between a principal surfaceof a thin film transistor substrate SUB1, which is a glass substrate,and a principal surface of a CF side flexible substrate F-SUB2, which isa plastic substrate, and bonding them together with a frame shaped sealagent SL encircling a display area.

A feature of the embodiment lies in adopting a structure in which awiring substrate FPC is sandwiched between the thin film transistorsubstrate SUB1, which is the glass substrate, and the CF side flexiblesubstrate F-SUB 2.

As shown in FIG. 4, the principal surface of the CF side flexiblesubstrate F-SUB2 has a silicon nitride layer (a second etch stopperlayer HFS2), which is a transparent inorganic insulating layer, attachedthereto with a second adhesive SL-2, and a color filter layer CF isprovided on the silicon nitride layer. The second adhesive SL-2 fills aspace outside the seal agent SL between the thin film transistorsubstrate SUB1 and the CF side flexible substrate F-SUB2, covering theheretofore described wiring connection portion TMA and the heretoforedescribed wiring substrate (the flexible printed substrate) FPCconnected thereto.

The seal agent SL and the second adhesive SL-2 are made of differentmaterials. The materials of the seal agent SL and second adhesive SL-2are the same as those of the embodiment 1.

FIGS. 5A to 5E are views illustrating a method of manufacturing theliquid crystal display device described in the embodiment 2 of theinvention. FIG. 5A, being a sectional view of a condition in which thethin film transistor substrate SUB1 and an opposite substrate SUB2 arecaused to face each other, shows a condition before the liquid crystalis sealed in. A pixel circuit configured of thin film transistors TFT isformed on the principal surface of the thin film transistor substrateSUB1.

A first etch stopper layer HFS1 and the second etch stopper layer HFS2are laminated, in this order, onto a principal surface of the oppositesubstrate SUB2. A color filter is formed on the second etch stopperlayer HFS2. An illustration of a black matrix or the like provided onthe opposite substrate SUB2 is omitted. Also, an oriented film is formedas a topmost layer on each substrate, but an illustration is omittedhere. The seal agent SL is formed encircling the display area of thethin film transistor substrate SUB1. The wiring substrate FPC isattached to the wiring connection portion TMA at one edge of the thinfilm transistor substrate SUB1.

Mo—W is suitable for the first etch stopper layer HFS1, while siliconnitride is suitable for the second etch stopper layer HFS2. The firstetch stopper layer HFS1 is insoluble in an etchant for the oppositesubstrate SUB2. Also, the second etch stopper layer HFS2 is insoluble inan etchant for the first etch stopper layer HFS1.

As shown in FIG. 5B, the principal surface of the opposite substrateSUB2 and the principal surface of the thin film transistor substrateSUB1 are bonded together, and the liquid crystal LC is sealed in withina bonding space. A perimeter of the space between the two substrates issealed with the seal agent SL.

In this condition, the opposite substrate SUB2 is dissolved and removed,by a full etching, with a glass dissolving etchant. At this time, anetching of the CF side second etch stopper layer HFS2 is stopped by theCF side first etch stopper layer HFS1 (FIG. 5C).

Next, the CF side first etch stopper layer HFS1 is dissolved and removedby a full etching (FIG. 5D). An etchant etching the CF side first etchstopper layer HFS1 does not etch the CF side second etch stopper layerHFS2. That is, the color filter CF is protected by the CF side secondetch stopper layer HFS2.

The second adhesive SL-2 is applied covering the CF side second etchstopper layer HFS2, the wiring connection portion TMA, and one portionof the wiring substrate FPC. The CF side flexible substrate F-SUB2,which is the plastic substrate, is attached with the second adhesiveSL-2 (FIG. 5E).

By the second adhesive SL-2 covering a terminal portion of the wiringsubstrate FPC, a stress concentration on the terminal portion of thewiring substrate FPC is avoided. The thin film transistor substrate SUB1is reduced in thickness by means of a polishing or the like whennecessary.

It is possible, through the heretofore described steps, to obtain theliquid crystal display device described in the embodiment 2 of theinvention.

1. A liquid crystal display device comprising: a first substrate; asecond substrate which sandwiches a liquid crystal between itself andthe first substrate; and a seal agent which, as well as bonding thefirst substrate and the second substrate together, seals the liquidcrystal, wherein the first substrate has thin film transistors and awiring connection portion in which are formed terminals connected to thethin film transistors, a wiring substrate connected to the terminals isdisposed in the wiring connection portion, the second substrate is aplastic substrate, and has an adhesive layer and an inorganic insulatinglayer formed on top of the adhesive layer, and the adhesive layer coversthe wiring connection portion and one portion of the wiring substrate.2. The liquid crystal display device according to claim 1, wherein thesecond substrate has a color filter layer on top of the inorganicinsulating layer.
 3. The liquid crystal display device according toclaim 1, wherein the wiring substrate is a flexible printed substrate.4. The liquid crystal display device according to claim 1, wherein theinorganic insulating layer is a silicon nitride layer.
 5. The liquidcrystal display device according to claim 1, wherein the first substrateis a plastic substrate, and has an adhesive layer and an inorganicinsulating layer formed on top of the adhesive layer, and the thin filmtransistors and the wiring connection portion are formed on theinorganic insulating layer on the first substrate.
 6. The liquid crystaldisplay device according to claim 1, wherein the first substrate is aglass substrate.
 7. The liquid crystal display device according to claim1, wherein a material of the seal agent and a material of the adhesivelayer are different.
 8. A method of manufacturing a liquid crystaldisplay device including a first plastic substrate, a second plasticsubstrate which sandwiches a liquid crystal between itself and the firstplastic substrate, and a seal agent which seals the liquid crystal, themethod comprising the steps of: laminating a first etch stopper layer,and a second etch stopper layer of which a material is different fromthat of the first etch stopper layer, in this order, onto a first glasssubstrate; forming thin film transistors, and a wiring connectionportion in which are formed terminals connected to the thin filmtransistors, on top of the first glass substrate side second etchstopper layer; disposing a wiring substrate connected to the terminalsin the wiring connection portion; laminating a first etch stopper layer,and a second etch stopper layer of which a material is different fromthat of the first etch stopper layer, in this order, onto a second glasssubstrate; etching the second glass substrate; etching the second glasssubstrate side first etch stopper layer; as well as attaching the secondplastic substrate to the second glass substrate side second etch stopperlayer by means of an adhesive layer, covering the wiring connectionportion and one portion of the wiring substrate with the adhesive layer;etching the first glass substrate; etching the first glass substrateside first etch stopper layer; and attaching the first flexiblesubstrate to the first glass substrate side second etch stopper layer bymeans of an adhesive layer.
 9. The liquid crystal display devicemanufacturing method according to claim 8, wherein a color filter layeris formed on top of the second glass substrate side second etch stopperlayer.
 10. The liquid crystal display device manufacturing methodaccording to claim 8, wherein the wiring substrate is a flexible printedsubstrate.
 11. The liquid crystal display device manufacturing methodaccording to claim 8, wherein a principal component of the first etchstopper layer is an Mo—W alloy, and the second etch stopper layer is asilicon nitride layer.
 12. The liquid crystal display devicemanufacturing method according to claim 8, wherein a material of theseal agent and a material of the adhesive layer are different.
 13. Amethod of manufacturing a liquid crystal display device including afirst glass substrate, a plastic substrate which sandwiches a liquidcrystal between itself and the first glass substrate, and a seal agentwhich seals the liquid crystal, the method comprising the steps of:forming thin film transistors, and a wiring connection portion in whichare formed terminals connected to the thin film transistors, on thefirst glass substrate; laminating a first etch stopper layer, and asecond etch stopper layer of which a material is different from that ofthe first etch stopper layer, in this order, onto a second glasssubstrate; etching the second glass substrate; etching the second glasssubstrate side first etch stopper layer; and as well as attaching theplastic substrate to the second glass substrate side second etch stopperlayer by means of an adhesive layer, covering the wiring connectionportion and one portion of the wiring substrate with the adhesive layer.14. The liquid crystal display device manufacturing method according toclaim 13, wherein a color filter layer is formed on top of the secondetch stopper layer.
 15. The liquid crystal display device manufacturingmethod according to claim 13, wherein the wiring substrate is a flexibleprinted substrate.
 16. The liquid crystal display device manufacturingmethod according to claim 13, wherein a principal component of the firstetch stopper layer is an Mo—W alloy, and the second etch stopper layeris a silicon nitride layer.
 17. The liquid crystal display devicemanufacturing method according to claim 13, wherein a material of theseal agent and a material of the adhesive layer are different.